An image sensor is an electronic device that converts an optical image into an electronic signal. It is used in digital cameras and imaging devices to convert the light received on the camera or imaging device lens into a digital image.
Techopedia explains Image Sensor
An image sensor is a device used primarily in standalone or embedded digital cameras and imaging devices. Typically, when light strikes the lens of a camera, the image sensor captures that light, converts it into an electronic signal and then transmits it to the camera or imaging device processor, which transforms the electronic signal into a digital image.